Field of the Invention
The present invention relates to a liquid discharge head that discharges a liquid from an orifice by making energy act on the liquid. In particular, the present invention relates to an inspection apparatus and method for inspecting the quality of driving of an energy generation element that is provided on the liquid discharge head and generates energy to discharge the liquid, and a liquid discharge head suitable for the inspection method.
Description of the Related Art
A liquid discharge head makes energy act on a liquid existing in a fluid channel and thus discharges the liquid from an orifice. To make energy act on the liquid in the fluid channel, an energy generation element is often provided in the vicinity of the fluid channel. The energy generation element is generally formed on one surface of a substrate made of, for example, silicon. The energy generation element is in contact with the liquid via a protection film formed on its surface, and is driven by a pulse-like electrical signal. The substrate on which the energy generation element is provided is called an element substrate. In a liquid discharge head of a type that applies thermal energy to a liquid to partially vaporize and expand the liquid and thus discharges the liquid from the orifice as a droplet, for example, a resistive heating element is used as the energy generation element. In a liquid discharge head of a type that makes mechanical energy directly act on a liquid, for example, a piezoelectric element is used as the energy generation element.
A representative example of the liquid discharge head is an inkjet print head that discharges an ink droplet to print. When the liquid discharge head is an inkjet print head, the energy generation element is particularly called a print element. In the inkjet print head, to achieve printing of higher image quality at a higher speed, print elements and orifices are arranged at a higher density, and a number of orifices are arrayed. Accordingly, the occurrence probability of a fault such as a rupture of a print element itself or disconnection of an electric wire provided on the element substrate and connected to a print element rises. Hence, inspection in the manufacturing process is one of important steps. Even during actual use after shipment, the occurrence frequency of a malfunction such as a rupture of a print element or disconnection of a wire rises as the use time accumulates. Hence, the inkjet print head is demanded to be inspectable even in an actual use environment.
Considering the above problems, print inspection by actually discharging ink is widely carried out for the inkjet print head in the manufacturing process or in an environment where the inkjet print head is actually used. In print inspection, the inkjet print head is driven to print a specific image pattern on a print medium such as a paper sheet surface. The print pattern formed on the print medium is visually recognized or read by an optical sensor and inspected.
Japanese Patent Laid-Open No. 2-208052 discloses, in a liquid discharge head using a resistive heating element, providing a detection circuit configured to detect the value of a current flowing to the resistive heating element on a wire that supplies power to the resistive heating element and detecting a rupture of the resistive heating element based on the current value detected by the detection circuit.
Japanese Patent Laid-Open No. 10-217471 discloses, as a method of inspecting an inkjet print head that uses conductive ink, a method of doing inspection by monitoring a voltage waveform applied to a print element by an electrode in an ink tank. In the method of Japanese Patent Laid-Open No. 10-217471, using a protection film provided on the surface of the print element as a capacitor, the voltage waveform is monitored via the capacitor and the ink that is a conducting path, and clogging in an ink channel, a rupture of a print element, or disconnection of an electric wire is inspected based on the obtained voltage waveform.
Out of the above-described inspection methods, print inspection in the inkjet print head can inspect whether discharge is normal or not but cannot determine whether the cause of a discharge error is an electrical failure such as a rupture of a print element or disconnection of a wire, or a fault in an orifice or an ink channel. For this reason, if deterioration of print quality has occurred during use, a recovery operation such as ink suction is performed regardless of the cause. If the cause is an electrical failure, ink and time are wasted.
According to the method of Japanese Patent Laid-Open No. 2-208052, it is possible to inspect an electrical failure in the inkjet print head. A detailed arrangement of the detection circuit is not mentioned in Japanese Patent Laid-Open No. 2-208052. As a general and simple arrangement, a current sensing resistor is inserted midway through a power supply line, and a voltage drop that occurs in accordance with a current value is measured by a voltmeter and inspected. In the inkjet print head, however, a smoothing capacitor is inserted in the power supply line to a print element. When performing inspection, the smoothing capacitor needs to be detached to detect an accurate current.
Inspection using the method of Japanese Patent Laid-Open No. 2-208052 is inspection performed under an operation condition including the voltage drop. In a strict sense, an actual operation is not reproduced in the inspection.
In the method of Japanese Patent Laid-Open No. 10-217471, both a discharge error caused by an electrical failure and a discharge error caused by a fault in an ink channel can be inspected using ink as a conductor. However, since the ON resistance of the ink variously changes in accordance with the amount or distribution of bubbles generated in the ink channel, quality determination may be difficult depending on the obtained voltage waveform. Since the electrode for detection needs to be provided in the ink tank, the cost of the ink tank becomes high. In addition, the method of Japanese Patent Laid-Open No. 10-217471 assumes use of conductive ink and is therefore hardly applicable to a general liquid discharge head that does not necessarily discharge a conductive liquid.